The present invention relates to indwelling catheters and electrode leads generally and more particularly to introducer systems for directing the placement or removal of fixed-screw catheters and electrode leads in a desired portion of a patient""s body.
Catheters and leads may be placed in a desired location in a patient""s body, particularly within the patient""s vasculature, by means of introducers, guide catheters or introducer catheters, hereafter referred to collectively as xe2x80x9cintroducersxe2x80x9d. These introducers typically include an elongated sheath, which is inserted into the blood vessel or other portion of the patient""s body, through which the lead or catheter is introduced. Recently, in conjunction with the development of smaller diameter cardiac pacing leads, there has been an increased level of interest in the use of introducers for lead placement. One type of pacing lead which has been proposed for placement by means of an introducer is the small diameter screw-in lead.
Small diameter screw-in leads have several desirable attributes, which are fully disclosed in U.S. Pat. No. 5,246,014, issued to Williams et al. Small-diameter leads, particularly those lacking an internal stylet or other torque transmitting member, tend to have little torsional rigidity and are difficult to screw into tissue using torque applied to the proximal end of the lead body. For such leads, as disclosed in the ""014 patent, it has been proposed to provide a mechanism that can impart the rotational torque needed to advance the fixation helix directly to the distal end of the lead body. In the ""014 patent, this mechanism takes the form of a tubular member which is adapted to engage the distal end of the lead body and which is rotatable within an associated introducer sheath. In the system disclosed in the ""014 patent, the lead was provided with a non-circular cross section at its distal tip, which engaged with a correspondingly formed recess at the distal end of the tubular member. Similar mechanisms have been proposed for introduction of fetal scalp electrodes, as disclosed in U.S. Pat. No. 3,827,428 issued to Hon et al.
The present invention provides an introducer or guide catheter system that may be used to correctly position a lead having a fixation helix rigidly mounted to the distal end of the lead body (fixed-screw lead) and rotate the fixation helix into body tissue. The introducer system may also be employed to introduce other types of leads or catheters into a patient""s body. If desired, the introducer may be used to extract leads as well.
In the preferred embodiments disclosed herein, the introducer includes flexible, tubular inner and outer sheaths. The inner sheath is configured to rotate within the outer sheath and serves as a tool for rotating the distal end of the lead and the fixation helix. The distal portion of the inner sheath is provided with a mechanism for gripping the distal portion of the lead body. The flexible outer sheath in a preferred embodiment is provided with a stylet lumen, in which stylets of pre-set curvatures or deflectable stylets may be inserted, in order to induce desired curvatures in the introducer system.
Unlike the system disclosed in the above-cited ""014 patent, the gripping mechanisms of the present invention may be used with leads having a circular cross section at their distal extremities. This capability of the gripping mechanisms allows the use of leads having smooth, iso-idametric profiles over their distal portions. In addition, this feature allows the inner sheath to grip the lead body at multiple locations proximal to the distal end of the lead, so that the distal end of the introducer system need not always be placed immediately adjacent the site at which location of the fixation helix is desired. A knob is attached to the proximal end of the inner sheath, enabling the physician to manipulate the gripping mechanism and screw the fixation helix into tissue and/or remove it from tissue.
In one embodiment of the invention, a filament braid serves as the gripping mechanism. In this embodiment, the physician pulls on the braid from the proximal (knob) end of the introducer to compress the braid around a distal portion of the lead body and thus grip the lead. The inner sheath and the braid are then rotated together to rotate the fixation helix. Alternative gripping mechanism embodiments include a coil and a wound cable, both of which when stretched contract to grip the distal portion of the lead body, and a wedge collett, which collapses to grip the distal portion of the lead body.
The inner sheath and gripping mechanisms of the present invention provide 1:1 torque transfer to the distal end of the lead, allowing easier fixation and/or detachment of the lead for repositioning. The introducer of the present invention may be used to position or remove fixed-screw leads used with bradycardia pacemakers, antitachyarrhythmia devices, or muscle or nerve stimulators. It is particularly beneficial for use in the placement or removal of fixed-screw transvenous leads or catheters with small diameter bodies and little or no torsional rigidity. It may, of course, also be used to position or extract other types of catheters in procedures in which the ability to precisely control rotation of the distal portion of the catheter is desirable.